The objective is to determine the nature and incidence of pathology lesions that develop throughout the life span of HSR/stroke prone rats. WKY rats will be used as controls. Animals of each sex will be examined at 3 months, 6 months, 9 months, 12 months and 15 months of age. Tissues will be studied by light microscopic methods and if indicated, electron microscopic technique. These strains have great potential as animal models for the study of cerebrovascular disease in human beings. This study involved only HSR/SP rats, so a new title was inserted to reflect that change.